1. Field of the Invention
This invention relates to a photo-sensitive and heat-sensitive composition which is devised to be fixed when irradiated with visible light and heated and generate color when irradiated with ultraviolet ray to thereby produce a high quality image directly by dry method, and a recording element comprising a support and a layer made of said composition superposed on said support.
2. Description of the Prior Art
A considerably large number of image-forming recording elements have been widely utilized or proposed up to now. As their typical instances there can be enumerated, for instance, diazo copying materials using alkali media as developers, photographic films using silver salts, etc. However, the above mentioned image-forming recording elements are defective in that developers and fixers must be used in order to obtain an image in practice.
As an attempt to eliminate the foregoing defects, accordingly, public attention has been attracted to dry photochemical photo-sensitive compositions and recording elements capable of forming images only with light as disclosed in Japanese Patent Publication Nos. 19161/1968, 40150/1970, 17855/1972, Japanese Laid Open Patent Application No. 12879/1972, etc. For instance, the photo-sensitive composition as disclosed in Japanese Patent Publication No. 19161/1968 comprises (a) photooxidant such as hexaarylbiimidazole, tetraarylhydrazine or the like, (b) a color-generator such as leuco-pigment, hydrazone or the like and (c) a binary system redox couple comprising an oxidant component such as quinone, ketone or the like and a reductant component such as alcohol, ester or the like or a one component system redox couple such as 1,4-bis (2-methoxyethyl) anthraquinone or the like. This photosensitive composition generates color when being subjected to light of specific wavelength such as ultraviolet ray, and its originally generated color is deactivated permanently, that is, fixed by light of different wavelength such as visible light. In this instance, the color generating reaction is performed by the action of photooxidant and color-generator and the fixing reaction is performed by the action of said redox couple. Accordingly, the use of the photo-sensitive composition of this type can obtain both positive image and negative image by selecting the sequence of irradiation of ultraviolet ray and visible light, but said photo-sensitive composition is defective in that the fixing sensitivity is extremely low as compared with the color generating sensitivity.
Japanese Patent Publication Nos. 139722/1975, 139723/1975, 139724/1975, etc. disclose each an image-forming recording element comprising a support and a photo-sensitive and heat-sensitive layer superposed thereon. The photo-sensitive and heat-sensitive composition used herein is mainly composed of (a) a cobalt (III) complex and (b) a photoreductant such as quinone, diazonium salt, disulfide or the like. In the case of the composition of this sort there is formed an image in such a manner that the photoreductant generates a reducing agent when irradiated with visible light and this agent reduces and discolors the cobalt (III) complex when heated (at the same time the cobalt (III) complex generates a basic substance such as ammonia or the like). Moreover, Japanese Patent Publication No. 139724/1975 proposes to accelerate the reduction of the cobalt (III) complex as well as promote the developed color density by the addition of a chelating agent such as nitroso-arol, dithiooxyamide or the like. In this connection, it is to be noted that the use of such a chelating agent-containing photo-sensitive and heat-sensitive composition is surely advantageous in that a high sensitive image can be obtained as compared with diazo copying materials by the aid of the oxidation reduction reaction between the cobalt (III) complex and the photoreductant, but on the other hand is defective in the following points, namely, (1) since the coloration of the composition is effected by the action of the generated cobalt (III) chelate complex compound there can be obtained only a negative image, (2) the obtained image undergoes severe thermal fog (in the heating step, the periphery of the exposed area generates color, too) and the like.